An air-driven hydraulic pump

ABSTRACT

An air-driven hydraulic pump, comprising an air motor, and an oil pump, which is operatively connected with the air motor, wherein the air motor includes a cylinder element in which an air piston is arranged movable in a reciprocating manner along a centre axis. The air piston is connected with an oil piston of the oil pump for transmitting the reciprocating movement of the air piston to the oil piston. The air piston separates a first cylinder chamber from a second cylinder chamber within the cylinder element. A control valve element is arranged to control the application of pressurized air from a source of pressurized air to the cylinder element. At least one pressure control valve is arranged in the air motor, allowing an air flow from one of the cylinder chambers to the other cylinder chamber when the pressure difference between the two cylinder chambers exceeds a predetermined value.

FIELD OF THE INVENTION

The present invention relates to an air-driven hydraulic pump, comprising an air motor which is operatively connected with an oil pump, wherein the air motor comprises a cylinder element in which an air piston is arranged movable in a reciprocating manner along an axis. The air piston is connected with an oil piston of the oil pump for transmitting the reciprocating movement of the air piston to the oil piston.

BACKGROUND OF THE INVENTION

Air-driven hydraulic pumps of this kind are used to set oil under a predetermined level of pressure. Depending on the maximum oil pressure required, the hydraulic pump is suitable for applications such as bolt tensioning, injecting oil for overcoming interference fits and pressurizing large hydraulic nuts. Compared to hand operated oil pumps, the use of air-driven oil pumps can save considerable time and effort.

The oil pump itself is driven by an air motor which allows to carry out a reciprocating movement of a piston within a respective cylinder. The piston of the air motor moves the piston of the oil pump. An air motor of this kind is known for example from U.S. Pat. No. 2,765,804. The air motor comprises a cylinder in which the air piston is arranged. The piston can carry out a reciprocating movement in the cylinder. The air piston separates two cylinder chambers in the cylinder. The cylinder chambers are periodically charged with pressurized air from a pressurized air source, wherein the periodical charging of the chambers with air is controlled by a control valve element.

Due to security reasons the pressure of the air for charging the air motor must be limited to limit also the pressure of the oil which is pressurized by the oil pump. Hence, typically an air-pressure limiter is arranged between the pressurized air source and the air motor. The user can however bypass the air-pressure limiter to obtain a higher oil pressure level which creates a high risk and must be prohibited.

SUMMARY OF THE INVENTION

It would be advantageous to be able to secure an air-driven hydraulic pump of the kind mentioned above against manipulations of the described manner.

To address this concern, in a first aspect of the invention there is provided an air-driven hydraulic pump, comprising an air motor, and an oil pump, which is operatively connected with the air motor. The air motor comprises a cylinder element in which an air piston is arranged movable in a reciprocating manner along a centre axis. The air piston is connected with an oil piston of the oil pump for transmitting the reciprocating movement of the air piston to the oil piston. The air piston separates a first cylinder chamber from a second cylinder chamber within the cylinder element. A control valve element is arranged to control the application of pressurized air from a source of pressurized air to the cylinder element. At least one pressure control valve is arranged in the air motor, allowing an air flow from one of the cylinder chambers to the other cylinder chamber when the pressure difference between the two cylinder chambers exceeds a predetermined value.

Thus, it has been made sure that no manipulation can take place, or at least it is substantially more difficult, and thus the risk of an accident is considerably reduced or even eliminated. The establishing of a limitation of the maximum operation pressure of the air motor is made in a tamper proof way, and thereby the safety during the use of the hydraulic pump is increased. By this solution it is made sure that even in the case that the air pump is charged with a too high pressure, e.g. by bypassing a pressure limiter before the air pump, limiting of the maximum oil pressure is reached as in this case an air flow can take place between the two cylinder chambers by means of the valve element

In accordance with an embodiment of the air-driven hydraulic pump, a single pressure control valve is employed.

In accordance with an embodiment of the air-driven hydraulic pump, the at least one pressure control valve is arranged in the air piston. The pressure control valve can then penetrate the air piston in the direction of the axis of the cylinder.

In accordance with an embodiment of the air-driven hydraulic pump, the at least one pressure control valve is a check valve. This check valve can comprise a housing in which a valve element is elastically biased, or biased, against a seat by means of a spring element. The valve element is preferably a ball. The spring element is preferably a helical spring. The housing can have a substantial hollow cylindrical form. The axis of the housing is mostly parallel to the axis of the cylinder element. Thereby, the axis of the housing and the axis of the cylinder element are preferably radially distanced from another.

In accordance with an embodiment of the air-driven pump, the at least one pressure control valve comprises means for adjusting the pressure difference between the two cylinder chambers at which the pressure control valve opens. The means for adjusting the pressure difference can comprise a screw element which is screwed into a thread in the housing of the valve element. The screw element can have a hexagon socket in one of its face sides for easy adjustment of the applied spring force.

In accordance with an embodiment of the air-driven hydraulic pump, the air piston and the oil piston are arranged coaxially.

Thus, even if an air pressure limiter is bypassed it is not possible to reach an inadmissible high oil pressure level.

Beneficially, any manipulation of the system is very difficult and thus the level of safety is high.

The cost for the equipment of the air motor with the proposed arrangement are quite low so that the invention proposal can be realized in a cost efficient way.

Thus, an air pressure limiter device is incorporated into the air-driven hydraulic pump. Thereby, the oil pressure that the pump is able to produce is limited, since the oil pressure is directly depending on the air pressure used for powering the air motor.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail and with reference to the appended drawings in which:

FIG. 1 shows a perspective view of en embodiment of the hydraulic pump according to this invention, consisting of an air motor and an oil pump;

FIG. 2 shows a top plan view of the hydraulic pump according FIG. 1;

FIG. 3 shows a cross sectional view along to the cut C-D according to FIG. 2;

FIG. 4 shows the detail “X” according to FIG. 3; and

FIG. 5 shows an enlarged view of the valve element as shown in FIG. 4.

DESCRIPTION OF EMBODIMENTS

In FIG. 1 an embodiment of the air-driven hydraulic pump 1 is shown which consists of an air motor 2 and an oil pump 3. The air motor 2 is supplied from a source 10 of pressurized air. The air is conducted into the air motor 2 by an air connection 19. The operation of the air motor 2 is influenced by an adjustor 20 for a control valve element which controls the air motor 2.

The hydraulic pump 1 has a carrying handle 25. In the region of this handle an oil inlet 21 is arranged which leads to the oil pump 3. The oil is set under pressure by the oil pump 3 and leaves it via a connection nipple 22. An oil return is denoted with reference numeral 23. A release valve 24 allows releasing the pressure from the oil pump 3. The pressure of the oil which is created by the oil pump 3 can be monitored with the pressure gauge 26.

Referring now to FIG. 2 and FIG. 3 it can be seen that the air motor 2 has a cylinder element 4 in which an air piston 5 is arranged movable in a reciprocating manner. The air piston 5 is connected with an oil piston 6 of the oil pump 3. The cylinder element 4 and the air piston 5 at one hand and the oil piston 6 at the other hand are arranged coaxially around a centre axis a of the cylinder element 4.

The air piston 5 divides the interior of the cylinder element 4 into two cylinder chambers in, i.e. a first cylinder chamber 7 and a second cylinder chamber 8. The air flow from the source 10 into the cylinder element 4 is controlled by a control valve element 9 in a well-known manner (see e.g. U.S. Pat. No. 2,765,804), typically in dependence of the axial position of the air piston (5) in the cylinder element (4).

To make sure that even during charging of the air motor 2 with a too high pressure no too high forces are exerted onto the oil piston 6, and thus to avoid the creation of a too high oil pressure, a pressure control valve 11 is arranged in the air motor 2. The pressure control valve 11 allows an air flow from one of the cylinder chambers 7, 8 to the other when the pressure difference between the two cylinder chambers 7, 8 exceeds a predetermined value.

More specifically, a pressure control valve 11 being a check valve is mounted into the air piston 5. Details of the pressure control valve 11 are apparent from FIG. 4 and FIG. 5.

The pressure control valve 11 has a housing 12 which has a substantial hollow cylindrical shape, i.e. a tube shape. The housing 12 has a centre axis b, which is parallel to the centre axis a of the cylinder element 4 but is radially spaced from it.

In the housing 12 a conical seat 14 is machined. A valve element 13, being a ball in the shown embodiment, is biased against the seat 14 by a helical spring 15. In FIG. 5 the pressure control valve 11 is shown in an opened state, i.e. a gap between the ball 13 and the seat 14 allows an air flow between the cylinder chambers 7, 8.

To adjust the pressure difference, between the left side and the right side of the pressure control valve 11 as shown in FIG. 5, at which the pressure control valve 11 opens, means 16, 17 are arranged for adjusting this pressure difference. The means comprise a screw element 16 which is screwed into a thread 17 which is machined in one of the axial end regions of the housing, as apparent from FIG. 5. For adjustment the screw element 16 has a hexagon socket 18 in its right face side. The screw element 16 can thus be moved axially relative to the housing. When the screw element 16 is moved to the left side in FIG. 5 the helical spring 15 is elastically biased with a higher force. Thus, the pressure difference between the cylinder chambers 7, 8 must be higher before the pressure control valves 11 opens.

Thus, the air from the source 10 acts via the control valve element 9 onto the air piston 5. The air piston 5 makes a reciprocating motion which in turn enables the oil piston 6 to suck, pressurize and deliver the oil to the desired application. The air pressure onto the air piston 5 dictates the maximum oil pressure that the oil pump 3 can deliver.

To limit the maximum air pressure available, the air pressure limiter valve, i.e. the pressure control valve 11, has been fitted to the air piston 5.

When the air pressure exceeds a predefined value the ball 13 is displaced from its seat 14, as the preset force of the spring element 15 is overcome. The overpressure air exhausts through the air piston 5 and is vented to the atmosphere.

The screw element 16 is preset by the manufacturer of the air-driven hydraulic pump 1 during the assembly of the whole system and corresponds with the required maximum air pressure which is allowed.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments.

For instance, more than one pressure control valve can be arranged, while a single valve is preferred, e.g. from a perspective of manufacturing costs.

Furthermore, the pressure control valve(s) can be arranged in a different way, while still being in the air motor, and while still letting air pass between the first and second chambers above a maximum pressure difference. The shown arrangement in the air piston is however presently preferred.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope. 

1-15. (canceled)
 16. An air-driven hydraulic pump, comprising an air motor, and an oil pump, which is operatively connected with the air motor, wherein the air motor comprises a cylinder element in which an air piston is arranged movable in a reciprocating manner along a centre axis, wherein the air piston is connected with an oil piston of the oil pump for transmitting the reciprocating movement of the air piston to the oil piston, wherein the air piston separates a first cylinder chamber from a second cylinder chamber within the cylinder element, wherein a control valve element is arranged to control an application of pressurized air from a source of pressurized air to the cylinder element, wherein at least one pressure control valve is arranged in the air motor, allowing an air flow from one of the cylinder chambers to the other cylinder chamber when a pressure difference between the two cylinder chambers exceeds a predetermined value.
 17. The air-driven hydraulic pump according to claim 16, wherein a single pressure control valve is arranged.
 18. The air-driven hydraulic pump according to claim 16, said at least one pressure control valve being arranged in the air piston.
 19. The air-driven hydraulic pump according to claim 18, said at least one pressure control valve penetrating the air piston in the direction of the centre axis.
 20. The air-driven hydraulic pump according to claim 16, said at least one pressure control valve being a check valve.
 21. The air-driven hydraulic pump according to claim 20, wherein the check valve comprises a housing in which a valve element is elastically biased against a seat by means of a spring element.
 22. The air-driven hydraulic pump according to claim 21, wherein the valve element is a ball.
 23. The air-driven hydraulic pump according to claim 21, wherein the spring element is a helical spring.
 24. The air-driven hydraulic pump according to claim 21, wherein the housing has a substantially hollow cylindrical form.
 25. The air-driven hydraulic pump according to claim 24, wherein an axis of the housing is parallel to the centre axis of the cylinder element.
 26. The air-driven hydraulic pump according to claim 25, wherein the axis of the housing and the centre axis of the cylinder element are radially distanced from each other.
 27. The air-driven hydraulic pump according to claim 16, said at least one pressure control valve comprising means for adjusting the pressure difference between the two cylinder chambers at which the at least one pressure control valve opens.
 28. The air-driven hydraulic pump according to claim 27, said means for adjusting the pressure difference comprising a screw element which is screwed into a thread in the housing.
 29. The air-driven hydraulic pump according to claim 28, wherein the screw element has a hexagon socket at one of its face sides.
 30. The air-driven hydraulic pump according to claim 16, wherein the air piston and the oil piston are arranged coaxially.
 31. The air-driven hydraulic pump according to claim 18, said at least one pressure control valve being a check valve.
 32. The air-driven hydraulic pump according to claim 18, said at least one pressure control valve comprising means for adjusting the pressure difference between the two cylinder chambers at which the at least one pressure control valve opens.
 33. The air-driven hydraulic pump according to claim 18, wherein the air piston and the oil piston are arranged coaxially.
 34. The air-driven hydraulic pump according to claim 19, wherein the air piston and the oil piston are arranged coaxially. 